Carrier 58MVP Error Code 45: Control Circuitry Lockout

What Does Code 45 Mean?

Status code 45 on the Carrier 58MVP is a control circuitry lockout caused by an internal failure on the control board. The lockout auto-resets after one hour, and the possible causes include a flame sense circuit failure, a gas valve relay stuck in the open position, or a software check error.

The flame sense circuit is the portion of the board that reads the microamp signal from the flame sensor. If this circuit fails, the board cannot determine whether a flame is present, making safe ignition impossible. A gas valve relay stuck open prevents the board from sending voltage to the gas valve, so the furnace cannot light even when all other conditions are met.

You can attempt a power reset by turning off the furnace breaker for 30 seconds and restoring power. If the code was caused by a transient software error, the reset may resolve it. However, if code 45 returns after the reset — whether immediately or within a few heating cycles — the control board has a hardware failure and needs to be replaced by a technician.

Common Causes

When to Call a Professional

Contact a licensed HVAC technician if:

• If the code reappears after resetting power — the control board needs replacement
• If the furnace remains locked out and does not resume operation

✓ Verified against manufacturer service manual — March 2026